Irbesartan is a known angiotensin II receptor antagonist (blocker). Angiotensin is an important participant in the renin-angiotensin-aldosterone system (RAAS) and has a strong influence on blood pressure. Irbesartan has the chemical name 2-butyl-3-[[2′-(1H-tetrazole-5-yl)biphenyl-4-yl]methyl]-1,3-diazaspiro[4.4]non-1-en-4-one. The structure of irbesartan is shown below (I).

The synthesis of irbesartan is discussed, inter alia, in U.S. Pat. Nos. 5,270,317 and 5,559,233; both of which are incorporated herein in their entirety by reference. In the synthesis therein disclosed, the prepenultimate reaction step (exclusive of work-up and purification) involves the reaction of a cyano group on the biphenyl ring with an azide, for example tributyltin azide. Reaction times as long as 210 hours can be required. See, e.g., '317 patent.
U.S. Pat. No. 5,629,331 also discloses a synthesis of irbesartan from a precursor 2-n-butyl-3-[(2′-cyanobiphenyl-4-yl)methyl]-1,3-diazaspiro[4.4]non-1-ene-4-one with sodium azide using a dipolar aprotic solvent. As acknowledged in the '331 patent, there are safety risks involved in the use of azides (column 4, line 39). Also, dipolar aprotic solvents (e.g. methylpyrrolidone) are relatively high boiling and can be difficult to remove.
There is a need for an improved synthetic route to irbesartan, its derivatives and its precursors.